Display device

ABSTRACT

The invention provides a display device using thin film type electron sources having a structure that can be formed in a simple manufacturing process. A lower electrode, a protective insulating layer and an interlayer film are formed on a cathode substrate. An upper bus electrode made from a laminated film of a metal film lower layer and a metal film upper layer is provided further on the interlayer film. A film of an upper electrode of a thin film type electron source for each pixel constituted by an insulating layer serving as an electron accelerating layer on the lower electrode and the upper electrode is formed on two stripe electrodes of the upper bus electrode in that pixel and another upper bus electrode in an adjacent pixel by sputtering. Then, the upper electrode is separated by self-alignment due to a setback portion of the metal film lower layer and an appentice of the metal film upper layer of the corresponding upper bus electrode. Thus, a thin film type electron source separated in accordance with each pixel is formed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a self-emitting flat panel typedisplay device, and particularly relates to a display device using thinfilm type electron source arrays.

[0003] 2. Description of the Related Art

[0004] An FED (Field Emission Display) using micro cold cathodes thatcan be integrated is known as one of self-emitting flat panel typedisplay devices using thin film type electron source arrays. The coldcathodes of FED are categorized into field emission type electronsources and hot electron type electron sources. The former includesSpindt type electron sources, surface conduction type electron sources,carbon-nanotube type electron sources, and the like. The latter includesthin film type electron sources of an MIM (Metal-Insulator-Metal) typecomprised of a metal-insulator-metal lamination, an MIS(Metal-Insulator-Semiconductor) type comprised of ametal-insulator-semiconductor lamination, ametal-insulator-semiconductor-metal type, and the like.

[0005] As the MIM type electron source, for example, an MIM typeelectron source disclosed in JP-A-7-65710 or JP-A-10-153979 is known. Asthe metal-insulator-semiconductor type electron source, an MOS typeelectron source reported in J. Vac. Sci. Technol. B11 (2) p. 429-432(1993) is known. As the metal-insulator-semiconductor-metal typeelectron source, an HEED type electron source reported inHigh-Efficiency-Electro-Emission Device, Jpn. J. Appl. Phys., Vol. 36,p. L939 or the like is known, an EL type electron source reported inElectroluminescence, OYO-BUTURI, Vol. 63, No. 6, p. 592 or the like isknown, or a porous silicon type electron source reported in OYO-BUTURI,Vol. 66, No. 5, p. 437 or the like is known. Incidentally, the MIM typeelectron source is disclosed in each of those documents.

[0006]FIG. 1 is a view for explaining the structure of an MIM typeelectron source and the principle of operation thereof. In FIG. 1, thereference numeral 11 represents a lower electrode; 13, an upperelectrode; 12, an insulating layer; and 23, a vacuum atmosphere. In thevacuum atmosphere, a driving voltage Vd is applied between the upperelectrode 13 and the lower electrode 11 so as to set the electric fieldin the insulating layer 12 to reach about 1-10 MV/cm. In this event,electrons e⁻ near the Fermi level in the lower electrode 11 penetrate abarrier due to a tunneling phenomenon, so as to be injected into aconducting band of the insulating layer 12 as an electron acceleratinglayer. Hot electrons formed thus flow into a conducting band of theupper electrode 13. Of the hot electrons, ones reaching the surface ofthe upper electrode 13 with energy not smaller than a work function φ ofthe upper electrode 13 are released to the vacuum 23.

[0007] It is desired that thin film type electron source arrays appliedto a display device or the like can be manufactured with a simplestructure and in a simple process in order to attain reduction in cost.A photolithographic method (also referred to as a photo-etching method)is conventionally used for processing thin film type electron sources.However, an exposure device used in a photolithographic process (alsoreferred to as a photo-process simply) is expensive. In addition,associated processes required before and after the photolithographicprocess, such as coating with resist, pre-baking, exposure, development,post-baking, removing, and cleansing, are long, and the process costthereof is high.

[0008] In contrast, if resist can be printed by screen printing or thelike, the cost of the manufacturing apparatus can be reduced. Inaddition, since the resist can be patterned directly, the processesrequired before and after the photolithographic process, such ascoating, pre-baking and development, can be omitted so that the processcost can be reduced. However, the resist patterning accuracy using theprinting method is incommensurably lower than the accuracy using thephoto-etching method. Thus, there is a problem in application of theprinting method to processing of conventional thin film type electronsources.

[0009] When a pattern involving the accuracy of pattern matching in onlyone lengthwise or crosswise direction is used, the processing accuracyin the resist patterning can be loosened and the printing method can beapplied easily in comparison with a pattern involving the accuracy ofpattern matching in both the lengthwise and crosswise directions. In thepresent invention, such a shape involving the accuracy of patternmatching in only one direction is referred to as “stripe shape” in thesense that the shape needs accuracy in only one dimension. In addition,an electrode having a stripe shape pattern is referred to as “stripeelectrode”. That is, the stripe electrode is a linear electrode having awidth with a structure having no hole, no convex portion, no concaveportion, no curved portion, etc. intentionally formed in the electrode.

[0010] Particularly, when a printing method such as screen printing,dispenser printing, inkjet printing or transfer printing is used as thepatterning method, the stripe electrode is preferred because the stripeelectrode is a little affected by deterioration of the patterningaccuracy caused by stretch of a screen, a blur of printed resist, or thelike.

BRIEF SUMMARY OF THE INVENTION

[0011] In order to reduce manufacturing cost of a display device, anobject of the present invention is to provide a thin film type electronsource using a stripe electrode easy to process in an image display areainvolving a pattern matching process, and to provide a display deviceusing such thin film type electron sources at a low cost.

[0012] In order to attain the foregoing object, according to the presentinvention, an electron accelerating layer of a thin film electron sourceis put between two adjacent stripe electrodes, and an upper electrode isdivided by self-alignment so as to attain pixel separation in the thinfilm electron source.

[0013] A thin film electron source can be produced using a stripeelectrode easy to pattern for each sub-pixel. Further, an upperelectrode can be processed by self-alignment. Thus, a display device canbe obtained at a low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a view for explaining the structure of an MIM typeelectron source and the principle of operation thereof;

[0015] FIGS. 2A-2C are diagrams for explaining a step for manufacturingan MIM electron source forming one pixel in a first embodiment of adisplay device according to the present invention;

[0016] FIGS. 3A-3C are diagrams for explaining a step for manufacturingthe MIM electron source forming one pixel in the first embodiment of thedisplay device according to the present invention, the step followingthe step in FIGS. 2A-2C;

[0017] FIGS. 4A-4C are diagrams for explaining a step for manufacturingthe MIM electron source forming one pixel in the first embodiment of thedisplay device according to the present invention, the step followingthe step in FIGS. 3A-3C;

[0018] FIGS. 5A-5C are diagrams for explaining a step for manufacturingthe MIM electron source forming one pixel in the first embodiment of thedisplay device according to the present invention, the step followingthe step in FIGS. 4A-4C;

[0019] FIGS. 6A-6C are diagrams for explaining a step for manufacturingthe MIM electron source forming one pixel in the first embodiment of thedisplay device according to the present invention, the step followingthe step in FIGS. 5A-5C;

[0020] FIGS. 7A-7C are diagrams for explaining a step for manufacturingthe MIM electron source forming one pixel in the first embodiment of thedisplay device according to the present invention, the step followingthe step in FIGS. 6A-6C;

[0021] FIGS. 8A-8C are diagrams for explaining a step for manufacturingthe MIM electron source forming one pixel in the first embodiment of thedisplay device according to the present invention, the step followingthe step in FIGS. 7A-7C;

[0022] FIGS. 9A-9C are diagrams for explaining a step for manufacturingthe MIM electron source forming one pixel in the first embodiment of thedisplay device according to the present invention, the step followingthe step in FIGS. 8A-8C;

[0023] FIGS. 10A-10C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the firstembodiment of the display device according to the present invention, thestep following the step in FIGS. 9A-9C;

[0024]FIG. 11 is a partially enlarged schematic plan view for explainingthe structure of the first embodiment of the display device according tothe present invention;

[0025] FIGS. 12A-12C are diagrams for explaining a step formanufacturing an MIM electron source forming one pixel in a secondembodiment of the display device according to the present invention;

[0026] FIGS. 13A-13C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the secondembodiment of the display device according to the present invention, thestep following the step in FIGS. 12A-12C;

[0027] FIGS. 14A-14C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the secondembodiment of the display device according to the present invention, thestep following the step in FIGS. 13A-13C;

[0028] FIGS. 15A-15C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the secondembodiment of the display device according to the present invention, thestep following the step in FIGS. 14A-14C;

[0029]FIG. 16 is a partially enlarged schematic plan view for explainingthe structure of the second embodiment of the display device accordingto the present invention;

[0030] FIGS. 17A-17C are diagrams for explaining a step formanufacturing an MIM electron source forming one pixel in a thirdembodiment of the display device according to the present invention;

[0031] FIGS. 18A-18C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the thirdembodiment of the display device according to the present invention, thestep following the step in FIGS. 17A-17C;

[0032] FIGS. 19A-19C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the thirdembodiment of the display device according to the present invention, thestep following the step in FIGS. 18A-18C;

[0033] FIGS. 20A-20C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the thirdembodiment of the display device according to the present invention, thestep following the step in FIGS. 19A-19C;

[0034]FIG. 21 is a partially enlarged schematic plan view for explainingthe structure of the third embodiment of the display device according tothe present invention;

[0035] FIGS. 22A-22C are diagrams for explaining a step formanufacturing an MIM electron source forming one pixel in a fourthembodiment of the display device according to the present invention;

[0036] FIGS. 23A-23C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the fourthembodiment of the display device according to the present invention, thestep following the step in FIGS. 22A-22C;

[0037] FIGS. 24A-24C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the fourthembodiment of the display device according to the present invention, thestep following the step in FIGS. 23A-23C;

[0038] FIGS. 25A-25C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the fourthembodiment of the display device according to the present invention, thestep following the step in FIGS. 24A-24C;

[0039] FIGS. 26A-26C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the fourthembodiment of the display device according to the present invention, thestep following the step in FIGS. 25A-25C;

[0040] FIGS. 27A-27C are diagrams for explaining a step formanufacturing the MIM electron source forming one pixel in the fourthembodiment of the display device according to the present invention, thestep following the step in FIGS. 26A-26C;

[0041]FIG. 28 is a partially enlarged schematic plan view for explainingthe structure of the fourth embodiment of the display device accordingto the present invention;

[0042] FIGS. 29A-29C are diagrams for explaining a step formanufacturing an MIM electron source forming one pixel in a fifthembodiment of the display device according to the present invention; and

[0043]FIG. 30 is a partially enlarged schematic plan view for explainingthe structure of the fifth embodiment of the display device according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0044] Embodiments of the present invention will be described below indetail with reference to the drawings.

[0045] First Embodiment

[0046] A first embodiment of the present invention using MIM electronsources will be described with reference to FIGS. 2A-2C to FIGS. 10A-10Cand FIG. 11. FIGS. 2A-2C to 10A-10C are diagrams for explainingmanufacturing steps of an MIM electron source forming one pictureelement in the first embodiment of a display device according to thepresent invention. The steps are illustrated in turn in FIGS. 2A-2C toFIGS. 10A-10C. FIGS. 2A-10A are plan views of one picture element. FIGS.2B-10B are sectional views taken on line A-A′ in FIGS. 2A-10Arespectively. FIGS. 2C-10C are sectional views taken on line B-B′ inFIGS. 2A-10A respectively. Incidentally, one picture element (alsoreferred to as “pixel”) here means a unit picture element for colordisplay. Each picture element is comprised of a plurality of sub-pictureelements (hereinafter referred to as “sub-pixels”) displaying differentprimary colors respectively. In this embodiment, the sub-pictureelements include three primary color sub-picture elements of red, greenand blue.

[0047] First, as shown in FIGS. 2A-2C, a metal film which will be madeinto lower electrodes 11 is formed on an insulating substrate (cathodesubstrate) 10 of glass or the like. Aluminum (Al) or an aluminum alloy(Al alloy) is used as the material of the lower electrodes 11. Thereason why Al or an AL alloy is used is that a high-quality insulatingfilm can be formed by anodization of these materials. In thisembodiment, an Al—Nd alloy doped with 2% by atomic weight of neodymium(Nd) is used. For example, a sputtering method is used for forming thefilm of the lower electrodes 11. The film thickness is set at 300 nm.After forming the film, stripe-shaped lower electrodes 11 are formed bya patterning step and an etching step (see FIGS. 3A-3C).

[0048] The electrode width of each lower electrode 11 varies accordingto the screen size and resolution of the display device, but is setsubstantially as large as the alignment pitch of its sub-pixels (about100-200 μm). The film of the lower electrodes 11 is etched, for example,by wet etching with a mixed aqueous solution of phosphoric acid, aceticacid and nitric acid. Since the lower electrodes 11 have a wide andsimple stripe shape, an inexpensive printing method can be used forpatterning resist for electrode processing. A screen printing method isused in this embodiment. Not to say, a comparatively inexpensivephoto-etching process such as proximity exposure can be used instead.Thus, reduction in cost can be attained in comparison with exposureusing a stepper, a projection aligner or the like.

[0049] Next, a protective insulating layer 14 and an insulating layer 12are formed for limiting each electron emitting portion to therebyprevent an electric field from concentrating on an edge of each lowerelectrode 11. First, a resist film 25 is applied to the portion whichwill bean electron emitting portion on each lower electrode 11, so thatthe lower electrode 11 is masked with the resist film 25. The portionwhich is not masked with the resist film 25 is anodized to beselectively thick so as to form the protective insulating layer 14(FIGS. 4A-4C). The resist film 25 used in this step has a shape as anelectron accelerating layer. It is therefore desired that the processingaccuracy is higher than that of the electrodes. To this end, the resistfilm 25 is patterned not in a printing method but in a photolithographicprocess using proximity exposure in this embodiment. When theanodization is performed with a formation voltage of 100V, theprotective insulating layer 14 is formed with a thickness of about 136nm.

[0050] Next, the resist film 25 is removed, and the remaining surface ofeach lower electrode 11 is anodized. For example, when the formationvoltage is 6V, the insulating layer 12 is formed with a thickness ofabout 10 nm on the lower electrode 11 (FIGS. 5A-5C).

[0051] Next, an interlayer film 15 is formed, and a metal film forforming upper bus electrodes 20 as feed lines to upper electrodes 13 isformed on the interlayer film 15, for example, in a sputtering method(FIGS. 6A-6C). For example, a silicon oxide film, a silicon nitridefilm, a silicon film or the like may be used as the interlayer film 15.In this embodiment, a silicon nitride film is used, and the filmthickness is set at 100 nm. The interlayer film 15 serves to fill uppossible pinholes in the protective insulating layer 14 formed byanodization so as to secure insulation between each lower electrode 11and each upper bus electrode.

[0052] The metal film serving as the upper bus electrodes 20 has astructure of a lamination of a metal film lower layer 16 and a metalfilm upper layer 18. For example, an Al—Nd alloy may be used for themetal film lower layer 16, and various metal materials such as copper(Cu) or chromium (Cr) may be used for the metal film upper layer 18. Inthis embodiment, an Al—Nd alloy is used as the material of the metalfilm lower layer 16, and Cu is used as the material of the metal filmupper layer 18.

[0053] Subsequently, the metal film upper layer 18 is processed into astripe shape crossing each lower electrode 11 by patterning of resistusing screen printing and an etching process. Stripe electrodes of themetal film upper layer 18 are formed so that one stripe electrode isformed in one pixel (FIGS. 7A-7C). Incidentally, other stripe electrodesadjacent to the stripe electrode illustrated by the metal film upperlayer 18 are not shown in FIG. 7A (the same thing will be applied to thefollowing embodiments).

[0054] Subsequently, the metal film lower layer 16 is processed into astripe shape crossing each lower electrode 11 by patterning of resistusing screen printing and an etching process. Stripe electrodes of themetal film lower layer 16 are also formed so that one stripe electrodeis formed in one pixel (FIGS. 8A-8C). At that time, the position of aresist film 26 printed is shifted in parallel with each stripe electrodeof the metal film upper layer 18 formed in FIGS. 7A-7C, so that theresist film 26 projects from the metal film upper layer 18 on one side(left side in FIG. 8C) of each stripe electrode of the metal film lowerlayer 16 so as to form a projecting portion 26A. Etching is suppressedby covering the metal film lower layer 16 with the projecting portion26A so that a contact portion 16A for securing connection with acorresponding upper electrode 13 which will be formed in a subsequentstep and will be described with reference to FIGS. 10A-10C is formed. Onthe opposite side (right side in FIG. 8C), an appentice 18A is formed inthe metal film upper layer 18 so as to serve as a mask with which asetback portion 16B for separating the upper electrodes 13 will beformed by over-etching of the metal film lower layer 16 in a subsequentstep. Thus, each upper bus electrode 20 (the laminated film of the metalfilm lower layer 16 and the metal film upper layer 18) for feeding powerto each upper electrode 13 can be formed.

[0055] Subsequently, as shown in FIGS. 9A-9C, the interlayer film 15 isprocessed to open each electron release portion. The electron releaseportion is formed in a part of the space surrounded by one lowerelectrode 11 in that pixel and two stripe-shaped upper bus electrodes 20(the illustrated upper bus electrode 20 and another not-illustratedupper bus electrode 20 adjacent thereto) crossing the lower electrode11. Patterning of resist at that time is performed using proximityexposure because the pattern is a hole pattern. In addition, etchingprocessing can be performed by dry etching using etching gas, forexample, having CF₄ or SF₆ as a chief component (FIGS. 9A-9C).

[0056] Finally, a film of the upper electrodes 13 shown in FIGS. 10A-10Cis formed. Although various methods can be adopted as the method forforming the film, sputtering from above the interlayer film 15 is usedin this embodiment. For example, a laminated film of iridium (Ir),platinum (Pt) and gold (Au) is used as the film of the upper electrodes13, and the thickness of the film is set at 6 nm. Incidentally, the filmthickness is not limited thereto. In this event, each upper electrode 13is cut on one side (right side in FIG. 10C) of the adjacentstripe-shaped upper bus electrode 20 by the appentice of the metal filmupper layer 18 thereof, so as to be separated in accordance with eachpixel. On the other hand, on the other side (left side in FIG. 10C) ofthe stripe-shaped upper bus electrode 20, the film serving as the upperelectrode 13 is formed continuously without disconnection to cover theinterlayer film 15 or the insulating layer 12 due to the contact portionof the metal film lower layer 16. Thus, a structure to feed power to theelectron source is arranged. The same thing about the formation of thefilm serving as the upper electrodes 13 is applied to the followingembodiments that will be described later.

[0057]FIG. 11 is a partially enlarged schematic plan view for explainingthe structure of the first embodiment of the display device according tothe present invention. Incidentally, parts having the same functions asthose in FIG. 1 and FIGS. 2A-2C to 10A-10C are denoted by the samereference numerals correspondingly. This display device is constitutedby a display panel in which a cathode-side substrate 10 (hereinafteralso referred to as “cathode substrate 10”) and a display-side substrate100 (hereinafter also referred to as “fluorescent screen substrate 100”)are laminated to each other (the same thing is applied to the followingembodiments). Incidentally, in FIG. 11, the fluorescent screen substrate100 is illustrated only partially in order to avoid complication, andparts of constituent members of the fluorescent screen formed in theinternal surface of the fluorescent screen substrate 100 are shown onthe cathode substrate 10. The fluorescent screen is formed out of redphosphor 111, green phosphor 112 and blue phosphor 113 sectioned by ablack matrix 120 in order to increase the contrast. In addition, a filmof an anode to which a high voltage of several kV is applied is formedin the internal surface of the fluorescent screen substrate 100.Incidentally, the anode is not shown in FIG. 11 (the same thing isapplied to the following embodiments).

[0058] For example, Y₂O₂S:Eu(P22-R), ZnS:Cu,Al(P22-G) andZnS:Ag,Cl(P22-B) may be used as the red, green, and blue phosphorsrespectively for forming the fluorescent screen. The black matrix 120 isformed in the internal surface of the display-side substrate 100 so asto surround the circumference of each color phosphor to thereby separatethe color phosphor from the other adjacent phosphors.

[0059] The cathode substrate 10 and the fluorescent screen substrate 100are laminated to each other through high-strength spacers 30 forsupporting the panel against the atmospheric pressure. Each of thespacers 30 is made of plate-like glass or ceramics given conductivity inorder to prevent electrostatic charge. The spacers 30 are disposed onthe metal film upper layer 18 forming the upper bus electrodes 20 of thecathode substrate 10, so as to be hidden under the black matrix 120 ofthe fluorescent screen substrate 100. The lower electrodes 11 areconnected to a signal line circuit 50 for supplying display signals(display data) to pixels, and the upper bus electrodes 20 formed out ofa laminated film of the metal film lower layer 16 and the metal filmupper layer 18 are connected to a scanning line circuit 60 for supplyingselection signals to the pixels. In each thin film type electron sourceconfigured thus, a voltage applied to a scanning line constituted by theupper bus electrode 20 is in a range of from several V to several tensV, which is sufficiently lower than the potential of the fluorescentscreen to which a voltage of several kV is applied. Thus, potentialsubstantially as low as the ground potential can be applied to thecathode side of each spacer 30. Accordingly, the upper bus electrode 20made from a laminated film of the metal film lower layer 16 and themetal film upper layer 18 can be also used as a spacer electrode. Inthis embodiment, the upper bus electrode 20 is also used as a spacerelectrode.

[0060] As is obvious from FIG. 11, in the circuit connection portionwhere connection is established between each lower electrode 11 and thesignal line circuit 50 and between each upper bus electrode 20 and thescanning line circuit 60 outside the image display area corresponding tothe area where the upper electrodes 13 are formed, the terminal pitch ofeach electrode typically differs from that in the image display area.Since there is no electron source in the circuit connection portion,pattern matching is not necessary. Therefore, each electrode in theconnection portion does not have to have a stripe shape. Thus, theelectrode in the connection portion can be processed in a printingmethod with low patterning accuracy, and typically does not have to beformed into a stripe shape.

[0061] In addition, as is obvious from FIG. 11, each thin film typeelectron source in an end portion of the image display area, that is,each thin film type electron source in the upper end row in FIG. 11 inthis embodiment has no adjacent pixel on the upper side. Thus, pixelseparation using two stripe electrodes is not required.

[0062] In such a manner, in the cathode structure of the display deviceaccording to this embodiment, each of the lower electrodes 11 serving assignal lines (data lines) and the upper bus electrodes 20 (laminatedfilm of the metal film lower layer 16 and the metal film upper layer 18)serving as both scanning lines and spacer electrodes is formed out ofone simple stripe electrode in one sub-pixel within the image displayarea. Further, the cathode structure has a function capable ofseparating the upper electrodes 13 by self-alignment. Thus, theelectrodes can be formed even by use of an inexpensive and low-accuracypatterning method such as a printing method.

[0063] Second Embodiment

[0064] Next, a second embodiment of the present invention using MIMelectron sources by way of example will be described with reference toFIGS. 2A-2C to 6A-6C, FIGS. 12A-12C to 15A-15C and FIG. 16. FIGS.12A-12C to 15A-15C are diagrams for explaining steps for manufacturingan MIM electron source forming one picture element in the secondembodiment of the display device according to the present invention. Thesteps are shown in turn along FIGS. 2A-2C to FIGS. 6A-6C and FIGS.12A-12C to 15A-15C. FIGS. 12A-15A are plan views of one picture element.FIGS. 12B-15B are sectional views taken on line A-A′ in FIGS. 12A-15Arespectively. FIGS. 12C-15C are sectional views taken on line B-B′ inFIGS. 12A-15A respectively. In addition, FIG. 16 is a partially enlargedschematic plan view for explaining the structure of the secondembodiment of the display device according to the present invention.Incidentally, parts having the same functions as those in the drawingsof the aforementioned embodiment are denoted by the same referencenumerals correspondingly.

[0065] First, a lower electrode 11, a protective insulating layer 14 andan insulating layer 12 are formed and an interlayer film 15, a metalfilm lower layer 16 and a metal film upper layer 18 (18′) are formedthereon in the same manner as the steps shown in FIGS. 2A-2C to 6A-6C inthe description of the first embodiment. Subsequently, the metal filmupper layer 18 (18′) of an upper bus electrode 20 is processed intostripe electrodes crossing the lower electrode 11 by patterning ofresist using screen printing and an etching process. Thus, two stripeelectrodes are formed in one pixel (FIGS. 12A-12C).

[0066] Subsequently, the metal film lower layer 16 of the upper buselectrode 20 is processed into stripe electrodes (metal film lowerlayers 16 and 16′) crossing the lower electrode 11 by patterning ofresist using screen printing and an etching process (FIGS. 13A-13C). Atthat time, as shown in FIG. 13C, the position of a resist film 26printed is shifted in parallel with the stripe electrode of the metalfilm upper layer 18 formed in FIGS. 12A-12C, so that the resist film 26projects from the metal film upper layer 18 on the insulating layer 12side (left side in FIG. 13C) so as to form a projecting portion 26A onone (metal film lower layer 16) of the stripe electrodes. Due to theprojecting portion 26A, a contact portion 16A for securing connectionbetween the upper electrode 13 and the metal film lower layer 16 as willbe formed in a subsequent step and as will be described with referenceto FIGS. 15A-15C is formed in the metal film lower layer 16.

[0067] On the opposite side (right side in FIG. 13C) to the insulatinglayer 12, an appentice 18A is formed in the metal film upper layer 18 soas to serve as a mask with which the metal film lower layer 16 is setback by over-etching. A setback portion 16B formed thus in the metalfilm lower layer 16 serves to separate an upper electrode 13 which willbe formed by sputtering in a subsequent step. Thus, an upper buselectrode 20 (a laminated film of the metal film lower layer 16 and themetal film upper layer 18) for feeding power to the upper electrode 13can be formed in each pixel. On the other hand, in the other metal filmupper layer 18′ serving as a stripe electrode disposed on the left sideof FIG. 13C, the metal film lower layer 16′ is over-etched both on theinsulating layer 12 side and on the opposite side thereto. Thus, themetal film lower layer 16′ is set back so that an appentice is formed oneach side of the metal film upper layer 18′. This appentice serves as amask for separating the upper electrode 13 which will be formed bysputtering in a subsequent step as will be described later withreference to FIGS. 15A-15C. Incidentally, this electrode (upper buselectrode 20 constituted by the metal film lower electrode 16′ and themetal film upper portion 18′) finally serves as a spacer electrode 21(FIG. 16) on which the spacers 30 are disposed.

[0068] Subsequently, the interlayer film 15 is processed to openelectron emission portions. Each electron emission portion is formed ina part of a crossing portion of the space surrounded by one lowerelectrode 11 in that pixel and two stripe-shaped electrodes (the upperbus electrode 20 constituted by the metal film lower layer 16 and themetal film upper layer 18 and the spacer electrode 21 constituted by themetal film lower layer 16′ and the metal film upper layer 18′) crossingthe lower electrode 11. The processing of opening the electron emissionportions can be performed by dry etching using etching gas, for example,having CF₄ or SF₆ as a chief component (FIGS. 14A-14C).

[0069] Finally, a film of the upper electrode 13 shown in FIGS. 15A-15Cis formed. A sputtering method is used for forming the film by way ofexample. For example, a laminated film of Ir, Pt and Au is used for thefilm of the upper electrode 13, and the thickness of the film is set at6 nm. In this event, the upper electrode 13 is cut by the appentices ofthe metal film upper layers 18 and 18′ of the two stripe electrodes (theupper bus electrode 20 and the spacer electrode 21), so as to beseparated in accordance with each pixel. On the other hand, on theinsulating layer 12 side of the upper bus electrode 20, the film servingas the upper electrode 13 is connected without disconnection due to thecontact portion 16A of the metal film lower layer 16. Thus, a structureto feed power over the interlayer film 15 and the insulating layer 12 isarranged.

[0070]FIG. 16 is a partially enlarged schematic plan view for explainingthe structure of the second embodiment of the display device accordingto the present invention. A fluorescent screen made from a black matrix120 for increasing the contrast, red phosphor 111, green phosphor 112and blue phosphor 113 is formed in the internal surface of a fluorescentscreen substrate 100. For example, Y₂O₂S:Eu(P22-R), ZnS:Cu,Al(P22-G) andZnS:Ag,Cl(P22-B) may be used as the red, green and blue phosphorsrespectively for forming the fluorescent screen. The black matrix 120 isformed in the internal surface of the display-side substrate 100 so asto surround the circumference of each color phosphor to thereby separatethe color phosphor from the other adjacent phosphors. In addition, afilm of an anode to which a high voltage of several kV is applied isformed in the internal surface of the fluorescent screen substrate 100.

[0071] The spacers 30 are disposed on the spacer electrode 21 of thecathode substrate 10 so as to be hidden under the black matrix 120 ofthe fluorescent screen substrate 100. Each lower electrode 11 isconnected to a signal line circuit 50, and each upper bus electrode 20(laminated film of the metal film lower layer 16 and the metal filmupper layer 18) is connected to a scanning line circuit 60. Eachlaminated film of the metal film lower layer 16′ and the metal filmupper layer 18′ serves as a spacer electrode 21, which is typicallygrounded.

[0072] As is obvious from FIG. 16, in the circuit connection portionwhere connection is established between each lower electrode 11 and thesignal line circuit 50 and between each upper bus electrode 20 and thescanning line circuit 60 outside the image display area corresponding tothe area where the upper electrodes 13 are formed, the terminal pitch ofeach electrode typically differs from that in the image display area.Since there is no electron source in the circuit connection portion,pattern matching is not necessary. Therefore, each electrode in theconnection portion does not have to have a stripe shape. Thus, theelectrode in the connection portion can be processed in a printingmethod with low patterning accuracy, and typically does not have to beformed into a stripe shape.

[0073] In addition, as is obvious from FIG. 16, each thin film typeelectron source in an end portion of the image display area, that is,each thin film type electron source in the upper end row in FIG. 16 inthis embodiment has no adjacent pixel on the upper side. Thus, pixelseparation using two stripe electrodes is not required.

[0074] In such a manner, in the cathode structure of the display deviceaccording to this embodiment, each of the lower electrodes 11 serving assignal lines (data lines), the upper bus electrodes 20 (laminated filmof the metal film lower layer 16 and the metal film upper layer 18)serving as scanning lines, and the spacer electrodes 21 (laminated filmof the metal film lower layer 16′ and the metal film upper layer 18′) isformed as one simple stripe electrode. Further, the cathode structurehas a function capable of separating the upper electrodes 13 byself-alignment. Thus, the electrodes can be formed even by use of aninexpensive and low-accuracy patterning method such as a printingmethod.

[0075] Third Embodiment

[0076] Next, a third embodiment of the display device according to thepresent invention using MIM electron sources by way of example will bedescribed with reference to FIGS. 2A-2C to 6A-6C, FIGS. 17A-17C to20A-20C and FIG. 21. FIGS. 17A-17C to 20A-20C are diagrams forexplaining steps for manufacturing an MIM electron source forming onepicture element in the third embodiment of the display device accordingto the present invention. FIGS. 17A-20A are plan views of one pictureelement. FIGS. 17B-20B are sectional views taken on line A-A′ in FIGS.17A-20A respectively. FIGS. 17C-20C are sectional views taken on lineB-B′ in FIGS. 17A-20A respectively. In addition, FIG. 21 is a partiallyenlarged schematic plan view for explaining the structure of the thirdembodiment of the display device according to the present invention.Incidentally, parts having the same functions as those in the drawingsof the aforementioned embodiments are denoted by the same referencenumerals correspondingly.

[0077] First, a lower electrode 11, a protective insulating layer 14 andan insulating layer 12 are formed and an interlayer film 15, a metalfilm lower layer 16 and a metal film upper layer 18 are formed thereonin the same manner as the steps shown in FIGS. 2A-2C to 6A-6C in thefirst embodiment.

[0078] Subsequently, the metal film upper layer 18 is processed intostripe electrodes crossing the lower electrode 11 by patterning ofresist using screen printing and an etching process. Thus, three stripeelectrodes (metal film upper layers 18, 18′ and 18″) are formed in onepixel (FIGS. 17A-17C).

[0079] Next, the metal film lower layer 16 is formed into stripeelectrodes (metal film lower layers 16, 16′ and 16″) crossing the lowerelectrode 11 by patterning of resist using screen printing and anetching process (FIGS. 18A-18C). At that time, in the same manner as inthe aforementioned embodiments, the positions of resist films 26 and 26′printed are shifted in parallel with the stripe electrodes of the metalfilm upper layers 18′ and 18″, formed in FIGS. 17A-17C, so that theresist films 26 and 26′ project from the metal film upper layers 18′ and18″ on the insulating layer 12 side respectively so as to formprojecting portions on two stripe electrodes (metal film lower layers16′ and 16″) having an insulating layer 12 put therebetween. Eachprojecting portion will serve as a contact portion for securingconnection with an upper electrode 13 in a subsequent step.

[0080] The insulating layer 12 is put between the metal film lowerlayers 16′ and 16″. On the other side of the metal film lower layer 16′,16″, opposite to the insulating layer 12, an appentice is formed withthe metal film upper layer 18′, 18″ as a mask so as to serve as a maskwith which the metal film lower layer 16′, 16″ will be over-etched toseparate the upper electrode 13 in a subsequent step. Thus, two upperbus electrodes (a laminated film of the metal film lower layer 16′ andthe metal film upper layer 18′ and a laminated film of the metal filmlower layer 16″ and the metal film upper layer 18″) for feeding power tothe upper electrode 13 can be formed. On the other hand, an appentice isformed on each side of the other stripe electrode (a laminated film ofthe metal film lower layer 16 and the metal film upper layer 18) withthe metal film upper layer 18 as a mask so as to serve as a mask forseparating the upper electrode 13. This electrode finally serves as aspacer electrode 21 on which spacers are disposed.

[0081] Subsequently, the interlayer film 15 is processed to openelectron emission portions (FIGS. 19A-19C). Each electron emissionportion is formed in a part of a crossing portion of the spacesurrounded by one lower electrode 11 in that pixel and two stripe-shapedelectrodes (one is a laminated film of the metal film lower layer 16′and the metal film upper layer 18′ and the other is a laminated film ofthe metal film lower layer 16″ and the metal film upper layer 18″)crossing the lower electrode 11 and forming contact portions 16′A and16″A. Etching the interlayer film 15 to thereby open the electronemission portions can be performed by dry etching using etching gas, forexample, having CF₄ or SF₆ as a chief component.

[0082] Finally, a film of the upper electrode 13 is formed as shown inFIGS. 20A-20C. A sputtering method is used for forming the film by wayof example. For example, a laminated film of Ir, Pt and Au is used asthe film of the upper electrode 13, and the thickness of the film is setat 6 nm. In this event, the upper electrode 13 is cut by the appenticesin the outside of the two upper bus electrodes (the laminated film ofthe metal film lower layer 16′ and the metal film upper layer 18′ andthe laminated film of the metal film lower layer 16″ and the metal filmupper layer 18″) having the contact portions 16′A and 16″A formedtherein respectively as shown in FIGS. 19A-19C, and by the appentice oneach side of the spacer electrode 21 (the laminated film of the metalfilm lower layer 16 and the metal film upper layer 18) so as to beseparated in accordance with each pixel. On the other hand, on theinsulating layer 12 side, the film serving as the upper electrode 13 isconnected without disconnection due to the contact portions 16′A and16″A of the metal film lower layers 16′ and 16″. Thus, a structure tofeed power over the interlayer film 15 and the insulating layer 12 isarranged.

[0083]FIG. 21 is a partially enlarged schematic plan view for explainingthe structure of the third embodiment of the display device according tothe present invention. A fluorescent screen made from a black matrix 120for increasing the contrast, red phosphor 111, green phosphor 112 andblue phosphor 113 is formed in the internal surface of a fluorescentscreen substrate 100. For example, Y₂O₂S:Eu(P22-R), ZnS:Cu,Al(P22-G) andZnS:Ag,Cl(P22-B) may be used as the red, green, and blue phosphorsrespectively for forming the fluorescent screen. The black matrix 120 isformed in the internal surface of the display-side substrate 100 so asto surround the circumference of each color phosphor to thereby separatethe color phosphor from the other adjacent phosphors. In addition, afilm of an anode to which a high voltage of several kV is applied isformed in the internal surface of the fluorescent screen substrate 100.

[0084] This embodiment is different from the first embodiment in thateach electron release portion is not close to the spacer electrode 21constituted by the metal film lower layer 16 and the metal film upperlayer 18. Accordingly, it is easy to position the spacer 30, and it isalso easy to increase the open area ratio of each phosphor. Further, anenough distance can be secured between the spacer 30 and the thin filmtype electron source. Thus, there is an advantage that the electroninflow to the spacer 30 is reduced so that the spacer 30 becomesdifficult to charge.

[0085] The lower electrodes 11 are connected to a signal line circuit50, and the upper bus electrodes (a laminated film of the metal filmlower layer 16′ and the metal film upper layer 18′ and a laminated filmof the metal film lower layer 16″, and the metal film upper layer 18″)are connected to a scanning line circuit 60. The spacer electrode 21comprised of a laminated film of the metal film lower layer 16 and themetal film upper layer 18 is typically grounded.

[0086] As is obvious from FIG. 21, in the circuit connection portionoutside the image display area corresponding to the area where the upperelectrodes 13 are formed, the terminal pitch of each electrode typicallydiffers from that in the image display area. Since there is no electronsource in the circuit connection portion, pattern matching is notnecessary. Therefore, each electrode in the connection portion does nothave to have a stripe shape. Thus, the electrode in the connectionportion can be processed in a printing method with low patterningaccuracy, and typically does not have to be formed into a stripe shape.

[0087] In such a manner, in the cathode structure according to thisembodiment, each of the lower electrodes 11, the upper bus electrodes 20and the spacer electrode 21 is formed as one simple stripe electrode.Further, the cathode structure has a function capable of separating theupper electrodes 13 by self-alignment. Thus, the electrodes can beformed even by use of an inexpensive and low-accuracy patterning methodsuch as a printing method. Further, the cathode structure isadvantageous in view of the positioning of the spacers 30 and theincreased open area ratio of the fluorescent screen.

[0088] Fourth Embodiment

[0089] Next, a fourth embodiment of the present invention using MIMelectron sources by way of example will be described with reference toFIGS. 2A-2C to 5A-5C, FIGS. 22A-22C to 27A-27C and FIG. 28. FIGS.22A-22C to 27A-27C are diagrams for explaining steps for manufacturingan MIM electron source forming one picture element in the fourthembodiment of the present invention. FIGS. 22A-27A are plan views of onepicture element. FIGS. 22B-27B are sectional views taken on line A-A′ inFIGS. 22A-27A respectively. FIGS. 22C-27C are sectional views taken online B-B′ in FIGS. 22A-27A respectively. In addition, FIG. 28 is apartially enlarged schematic plan view for explaining the structure ofthe fourth embodiment of the display device according to the presentinvention. Incidentally, parts having the same functions as those in thedrawings of the aforementioned embodiments are denoted by the samereference numerals correspondingly.

[0090] First, a lower electrode 11, a protective insulating layer 14 andan insulating layer 12 are formed in the same manner as the steps shownin FIGS. 2A-2C to 5A-5C in the first embodiment. Next, as shown in FIGS.22A-22C, an interlayer film 15 and a metal film are formed, for example,in a sputtering method or the like. The metal film serves as an upperbus electrode which will be a power feeder to upper electrodes 13 and aspacer electrode on which spacers will be disposed. For example, asilicon oxide film, a silicon nitride film, a silicon film or the likemay be used as the interlayer film 15. In this embodiment, a siliconnitride film is used, and the film thickness is set at 100 nm. Theinterlayer film 15 serves to fill up possible pinholes in the protectiveinsulating layer 14 formed by anodization, so as to secure insulationbetween each lower electrode 11 and each upper bus electrode.

[0091] In this embodiment, the upper bus electrode is formed as athree-layer laminated film in which Cu as a metal film intermediatelayer 17 is inserted between a metal film lower layer 16 and a metalfilm upper layer 18. The laminated film is not limited to such athree-layer laminated film, but may include four or more layers. A metalmaterial high in oxidation resistance, such as Al, chromium (Cr),tungsten (W) or molybdenum (Mo), an alloy containing those materials, ora laminated film of those materials may be used for the metal film lowerlayer 16 and the metal film upper layer 18. Incidentally, in thisembodiment, an Al—Nd alloy is used for the metal film lower layer 16 andthe metal film upper layer 18. Alternatively, a five-layer film using alaminated film of Cr, W, Mo or the like and an Al alloy as the metalfilm lower layer 16, a laminated film of Cr, W, Mo or the like and an Alalloy as the metal film upper layer 18, and high-melting metal for filmsin contact with Cu of the metal film intermediate layer 17 may be used.In this case, the high-melting metal serves as a barrier film in theheating step in the manufacturing process of the display device, so thatalloying of Al and Cu can be suppressed. Thus, such a five-layer film iseffective particularly in reducing in resistance.

[0092] When only the Al—Nd alloy is used, the film thickness of theAl—Nd alloy is set so that the metal film upper layer 18 is thicker thanthe metal film lower layer 16, and Cu of the metal film intermediatelayer 17 is as thick as possible in order to reduce the wiringresistance thereof. In this embodiment, the thickness of the metal filmlower layer 16 is set at 300 nm, the thickness of the metal filmintermediate layer is set at 17, 4 μm, and the thickness of the metalfilm upper layer 18 is set at 450 nm. Incidentally, Cu of the metal filmintermediate layer 17 may be formed by electroplating or the like aswell as sputtering.

[0093] In the case of the five-layer film using high-melting metal, itis particularly effective that a laminated film in which Cu is insertedbetween pieces of Mo and which can be wet-etched with a mixed aqueoussolution of phosphoric acid, acetic acid and nitric acid, is used as themetal film intermediate layer 17 in the same manner as Cu. In this case,each Mo film into which Cu is inserted is set to be 50 nm thick, and theAl alloy films as the metal film lower layer 16 and the metal film upperlayer 18 having the metal film intermediate layer 17 put therebetweenare set to be 300 nm thick and 50 nm thick respectively.

[0094] Subsequently, the metal film upper layer 18 is processed into astripe shape crossing the lower electrode 11 by patterning of resistusing screen printing and an etching process, as shown in FIGS. 23A-23C.In this etching process, for example, wet etching with a mixed aqueoussolution of phosphoric acid and acetic acid is used. Since nitric acidis not added to the etchant, Cu is not etched but only the Al—Nd alloycan be selectively etched.

[0095] Also in the case of the five-layer film using Mo, when nitricacid is not added to the etchant, Mo and Cu is not etched but only theAl—Nd alloy can be selectively etched. In this embodiment, one piece ofthe metal film upper layer 18 is formed in each pixel in the same manneras in the first embodiment, but two pieces may be formed in the samemanner as in the second embodiment.

[0096] Subsequently, using the same resist film as it is, or using theAl—Nd alloy of the metal film upper layer 18 as a mask, Cu of the metalfilm intermediate layer 17 is wet-etched, for example, with a mixedaqueous solution of phosphoric acid, acetic acid and nitric acid (FIGS.24A-24C). The etching rate of Cu in the etchant of the mixed aqueoussolution of phosphoric acid, acetic acid and nitric acid is much higherthan that of the Al—Nd alloy. Thus, only Cu of the metal filmintermediate layer 17 can be etched selectively. Also in the case of thefive-layer film using Mo, the etching rate of Mo and Cu is much higherthan that of the Al—Nd alloy. Thus, only the three-layer laminated filmof Mo and Cu can be etched selectively. Alternatively, an ammoniumpersulfate aqueous solution or a sodium persulfate aqueous solution isalso effective in etching Cu.

[0097] Subsequently, the metal film lower layer 16 is processed into astripe shape crossing the lower electrode 11 by patterning of resistusing screen printing and an etching process (FIGS. 25A-25C). Theetching process is performed with a mixed aqueous solution of phosphoricacid and acetic acid. At that time, the position of a resist film 26printed is shifted in parallel with the stripe electrode of the metalfilm upper layer 18 formed in FIGS. 23A-23C, so that the resulting metalfilm lower layer 16 projects from the metal film upper layer 18 on oneside (left side of FIG. 25C) so as to form a contact portion 16A forsecuring connection with the upper electrode 13 in a subsequent step. Onthe other side (right side of FIG. 25C) of the metal film lower layer16, over-etching is performed with the metal film upper layer 18 and themetal film intermediate layer 17 as a mask so as to set back the metalfilm lower layer 16 as if an appentice is formed in the metal filmintermediate layer 17. Thus, a setback portion 16B is formed.

[0098] The appentice of the metal film intermediate layer 17 serves toseparate the film of the upper electrode 13 formed in a subsequent step.At that time, since the metal film upper layer 18 is made thicker thanthe metal film lower layer 16, the metal film upper layer 18 can be lefton Cu of the metal film intermediate layer 17 even after the etching ofthe metal film lower layer 16. Thus, the surface of Cu can be protectedso that the oxidation resistance can be secured in spite of use of Cu,and the upper electrode 13 can be separated by self-alignment, while anupper bus electrode 0.20 for feeding power to the upper electrode 13 canbe formed. In the case where the five-layer film having Cu put betweenpieces of Mo is used as the metal film intermediate layer 17, Mo cansuppress the oxidization of Cu even if the Al alloy of the metal filmupper layer 18 is thin. Thus, it is not always necessary to make themetal film upper layer 18 thicker than the metal film lower layer 16.

[0099] Subsequently, the interlayer film 15 is processed to openelectron emission portions. Each electron emission portion is formed ina part of a crossing portion of the space surrounded by one lowerelectrode 11 in the pixel and two upper bus electrodes (one is alaminated film of the metal film lower layer 16, the metal filmintermediate layer 17 and the metal film upper layer 18 and the other isa laminated film of the metal film lower layer 16, the metal filmintermediate layer 17 and the metal film upper layer 18 in a not-shownadjacent pixel) crossing the lower electrode 11. This etching can beperformed by dry etching using etching gas, for example, having CF₄ orSF₆ as a chief component (FIGS. 26A-26C).

[0100] Finally, a film of the upper electrode 13 is formed. A sputteringmethod is used for forming the film in this embodiment. For example, alaminated film of Ir, Pt and Au is used as the film of the upperelectrode 13, and the thickness of the film is set at 6 nm. In thisevent, the upper electrode 13 is cut by the setback portion 16B of themetal film lower layer 16 based on the appentice structure of the metalfilm intermediate layer 17 and the metal film upper layer 18 on one side(right side in FIG. 27C) of the two upper bus electrodes (the laminatedfilm of the metal film lower layer 16, the metal film intermediate layer17 and the metal film upper layer 18) having an electron emissionportion put therebetween. On the other side (left side in FIG. 27C) ofthe two upper bus electrodes, the film serving as the upper electrode 13is connected to the upper bus electrode (the laminated film of the metalfilm lower layer 16, the metal film intermediate layer 17 and the metalfilm upper layer 18) without disconnection due to the contact portion16A of the metal film lower layer 16. Thus, a structure to feed power tothe electron release portion is arranged (FIGS. 27A-27C).

[0101]FIG. 28 is a partially enlarged schematic plan view for explainingthe structure of the fourth embodiment of the display device accordingto the present invention. In the same manner as in the aforementionedembodiments, a black matrix 120 for increasing the contrast, redphosphor 111, green phosphor 112 and blue phosphor 113 are formed in afluorescent screen substrate 100. For example, Y₂O₂S:Eu(P22-R),ZnS:Cu,Al(P22-G) and ZnS:Ag,Cl(P22-B) may be used as the red, green andblue phosphors respectively. The black matrix 120 is formed in theinternal surface of the display-side substrate 100 so as to surround thecircumference of each color phosphor to thereby separate the colorphosphor from the other adjacent phosphors. In order to avoidcomplication of the drawing, the black matrix and the phosphors of therespective colors are shown in only a part of the image display area. Inaddition, a film of an anode to which a high voltage of several kV isapplied is formed in the internal surface of the fluorescent screensubstrate 100.

[0102] The spacers 30 are disposed on the upper bus electrode 20 of thecathode substrate 10 so as to be hidden under the black matrix 120 ofthe fluorescent screen substrate 100. Each lower electrode 11 isconnected to a signal line circuit 50, and each upper bus electrode 20is connected to a scanning line circuit 60. In each thin film typeelectron source configured thus, a voltage applied to the upper buselectrode 20 serving as a scanning line is in a range of from several Vto several tens V, which is sufficiently lower than a voltage of severalkV to be applied to the anode of the fluorescent screen substrate 100.Thus, potential substantially as low as the ground potential can beapplied to the anode side of each spacer 30.

[0103] As is obvious from FIG. 28, in the circuit connection portionoutside the image display area corresponding to the area where the upperelectrodes 13 are formed, the electrode terminal pitch of the lowerelectrodes 11 or the upper bus electrodes 20 typically differs from thatin the image display area. Since there is no electron source in thecircuit connection portion, pattern matching is not necessary.Therefore, each electrode terminal in the connection portion does nothave to have a stripe shape. Thus, the electrode terminal in theconnection portion can be processed in a printing method with a lowpatterning accuracy and typically does not have to have a stripe shape.

[0104] In addition, as is obvious from FIG. 28, each thin film typeelectron source in an end portion of the image display area (each thinfilm type electron source in the upper end row in FIG. 28 in thisembodiment) has no adjacent pixel. Thus, pixel separation using twostripe electrodes as in the image display area is not required.

[0105] In such a manner, in the cathode structure forming the displaydevice according to this embodiment, due to the structure of a laminatedfilm in which low-resistance Cu wiring is put between pieces of an Alalloy, Cr or the like having oxidization resistance, the upper electrode13 can be processed by self-alignment, and the upper bus electrode(laminated film of the metal film lower layer 16, and the metal filmintermediate layer 17 and the metal film upper layer 18) prevented fromdeteriorating even in a sealing step can be produced. Thus, a voltagedrop due to the wiring resistance of the display device can besuppressed. Particularly when a five-layer laminated film structure inwhich high-melting metal such as Mo is inserted between an Al alloy andCu is used, alloying reaction between Al and Cu can be prevented so thatthe wiring resistance can be kept low specially.

[0106] In addition, due to the thick upper bus electrode (laminated filmof the metal film lower layer 16, and the metal film intermediate layer17 and the metal film upper layer 18), the thin film type electronsources can be prevented from being mechanically damaged by the spacersbearing the atmosphere.

[0107] Fifth Embodiment

[0108] Next, a fifth embodiment of the present invention using MIMelectron sources by way of example will be described with reference toFIGS. 2A-2C to 5A-5C, FIGS. 22A-22C to 27A-27C, FIGS. 29A-29C and FIG.30. FIGS. 29A-29C show a step for manufacturing an MIM electron sourceforming one picture element in the fifth embodiment of the displaydevice according to the present invention. FIG. 29A is a plan view ofone picture element. FIG. 29B is a sectional view taken on line A-A′ inFIG. 29A. FIG. 29C is a sectional view taken on line B-B′ in FIG. 29A.In addition, FIG. 30 is a partially enlarged schematic plan view forexplaining the structure of the fifth embodiment of the display deviceaccording to the present invention. Incidentally, parts having the samefunctions as those in the drawings of the aforementioned embodiments aredenoted by the same reference numerals correspondingly.

[0109] First, steps until forming the film of an upper electrode 13 areperformed in the same manner as that in the description of FIGS. 2A-2Cto 5A-5C and FIGS. 22A-22C to 27A-27C in the fourth embodiment.Subsequently, a paste containing a metal material such as silver (Ag)and a glass material is printed on an upper bus electrode (a laminatedfilm of a metal film lower layer 16, a metal film intermediate layer 17and a metal film upper layer 18) in a screen printing method, adispenser method, an inkjet method or the like, so as to form a thickfilm electrode 22. The thick film electrode 22 can be made about 10-20μm thick enough to reduce the wiring resistance and absorb the pressurefrom spacers. Further, the conductive properties of the thick filmelectrode 22 prevents the spacers from being charged, while the spacerscan be fixed firmly by baking the glass contained in the thick filmelectrode 22. The thick film electrode 22 is baked in a high temperatureprocess when sealing is secured between the thick film electrode 22 andthe fluorescent screen substrate 100 after the thick film electrode 22is dried. Thus, low resistance and bonding with the spacers are attained(FIGS. 29A-29C). The formation of the film of the upper electrode 13 isperformed in the same manner as in the aforementioned embodiments.

[0110]FIG. 30 is a partially enlarged schematic plan view for explainingthe structure of the fifth embodiment of the display device according tothe present invention. In the same manner as in the aforementionedembodiments, a black matrix 120 for increasing the contrast, redphosphor 111, green phosphor 112 and blue phosphor 113 are formed in afluorescent screen substrate 100. For example, Y₂O₂S:Eu(P22-R),ZnS:Cu,Al(P22-G) and ZnS:Ag,Cl(P22-B) may be used as the red, green andblue phosphors respectively. The black matrix 120 is formed in theinternal surface of the display-side substrate 100 so as to surround thecircumference of each color phosphor to thereby separate the colorphosphor from the other adjacent phosphors. In order to avoidcomplication of the drawing, the black matrix and the phosphors of therespective colors are shown in only a part of the image display area. Inaddition, a film of an anode to which a high voltage of several kV isapplied is formed in the internal surface of the fluorescent screensubstrate 100.

[0111] The spacers 30 are disposed on the thick film electrode 22 formedon the cathode substrate 10 so as to be hidden under the black matrix120 formed in the fluorescent screen substrate 100. Each lower electrode11 is connected to a signal line circuit 50, and each thick filmelectrode 22 is connected to a scanning line circuit 60. In each thinfilm type electron source configured thus, a voltage applied to thethick film electrode 22 serving as a scanning line is in a range of fromseveral V to several tens V, which is sufficiently lower than a voltageof several kV to be applied to the anode of the fluorescent screen.Thus, potential substantially as low as the ground potential can beapplied to the cathode side of each spacer.

[0112] As is obvious from FIG. 30, in the circuit connection portionoutside the image display area corresponding to the area where the upperelectrodes 13 are formed, the electrode terminal pitch of the lowerelectrodes 11 or the upper bus electrodes 20 typically differs from thatin the image display area. Since there is no electron source in thecircuit connection portion, pattern matching is not necessary.Therefore, each electrode terminal in the connection portion does nothave to have a stripe shape. Thus, each electrode terminal in theconnection portion can be processed in a printing method with a lowpatterning accuracy and typically does not have to have a stripe shape.

[0113] In addition, as is obvious from FIG. 30, each thin film typeelectron source in an end portion of the image display area (each thinfilm type electron source in the upper end row in FIG. 30 in thisembodiment) has no adjacent pixel. Thus, pixel separation using twostripe electrodes as in the inside of the image display area is notrequired.

[0114] In such a manner, in the cathode structure forming the displaydevice according to this embodiment, due to the thick film paste of Agor the like printed on the upper bus electrode, a voltage drop due tothe wiring resistance of the display device can be suppressed. Inaddition, the thick film electrode 22 is thick enough to absorb thepressure of each spacer 30. Thus, each thin film electron source can beprevented from being mechanically damaged by the spacer 30.

What is claimed is:
 1. A display device comprising: a display panelcomprised of a cathode substrate and a fluorescent screen substrate,said cathode substrate including an array of thin-film type electronsources each having a lower electrode, an upper electrode and anelectron accelerating layer retained between said lower electrode andsaid upper electrode, each of said electron sources radiating electronsfrom said upper electrode in response to a voltage applied between saidlower electrode and said upper electrode, said fluorescent screensubstrate including a fluorescent screen in which phosphors excited bysaid electrons to thereby emit light are formed; and a drive circuit fordriving said lower electrode and said upper electrode; wherein one ofsaid lower electrode and an upper bus electrode is a stripe-shapedelectrode in an image display area where said array of thin-film typeelectron sources of said display panel are disposed in a matrix, saidupper bus electrode being provided to feed power to said upperelectrode.
 2. A display device comprising: a display panel comprised ofa cathode substrate and a fluorescent screen substrate, said cathodesubstrate including an array of thin-film type electron sources eachhaving a lower electrode, an upper electrode and an electronaccelerating layer retained between said lower electrode and said upperelectrode, each of said electron sources radiating electrons from saidupper electrode in response to a voltage applied between said lowerelectrode and said upper electrode, said fluorescent screen substrateincluding a fluorescent screen in which phosphors excited by saidelectrons to thereby emit light are formed; and a drive circuit fordriving said lower electrode and said upper electrode; wherein both saidlower electrode and an upper bus electrode are stripe-shaped electrodesin an image display area where said array of thin-film type electronsources of said display panel are disposed in a matrix, said upper buselectrode being provided to feed power to said upper electrode.
 3. Adisplay device comprising: a display panel comprised of a cathodesubstrate and a fluorescent screen substrate, said cathode substrateincluding an array of thin-film type electron sources each having alower electrode, an upper electrode and an electron accelerating layerretained between said lower electrode and said upper electrode, each ofsaid electron sources radiating electrons from said upper electrode inresponse to a voltage applied between said lower electrode and saidupper electrode, said fluorescent screen substrate including afluorescent screen in which phosphors excited by said electrons tothereby emit light are formed; and a drive circuit for driving saidlower electrode and said upper electrode; wherein each of said thin-filmtype electron sources is provided between adjacent ones of stripe-shapedupper bus electrodes at least in an image display area; wherein saidupper electrode formed as a film in said image display area is connectedto one of said upper bus electrodes in a corresponding pixel, andseparated from other upper bus electrodes in adjacent pixels, so thatindividual pixels are separated from each other.
 4. A display devicecomprising: a display panel comprised of a cathode substrate and afluorescent screen substrate, said cathode substrate including an arrayof thin-film type electron sources each having a lower electrode, anupper electrode and an electron accelerating layer retained between saidlower electrode and said upper electrode, each of said electron sourcesradiating electrons from said upper electrode in response to a voltageapplied between said lower electrode and said upper electrode, saidfluorescent screen substrate including a fluorescent screen in whichphosphors excited by said electrons to thereby emit light are formed;and a drive circuit for driving said lower electrode and said upperelectrode; wherein each of said thin-film type electron sources isprovided between adjacent ones of stripe-shaped upper bus electrodes atleast in an image display area; wherein a film of said upper electrodeformed in said image display area is connected to one of said upper buselectrodes in a corresponding pixel, and separated from other upper buselectrodes in adjacent pixels due to a step of an appentice structureformed on one side surface of said upper bus electrode in saidcorresponding pixel, so that individual pixels are separated from eachother.
 5. A display device according to claim 3 or 4, wherein saidstripe-shaped upper bus electrodes are formed one by one per pixel inaccordance with a pitch of pixels, and each of said stripe-shaped upperbus electrodes has not only a function as said upper bus electrode forfeeding power to said upper electrode but also a function as anelectrode for giving potential to spacers inserted between said cathodesubstrate and said fluorescent screen substrate for supporting said twosubstrates.
 6. A display device comprising: a display panel comprised ofa cathode substrate and a fluorescent screen substrate, said cathodesubstrate including an array of thin-film type electron sources eachhaving a lower electrode, an upper electrode and an electronaccelerating layer retained between said lower electrode and said upperelectrode, each of said electron sources radiating electrons from saidupper electrode in response to a voltage applied between said lowerelectrode and said upper electrode, said fluorescent screen substrateincluding a fluorescent screen in which phosphors excited by saidelectrons to thereby emit light are formed; and a drive circuit fordriving said lower electrode and said upper electrode; wherein each ofsaid thin film type electron sources is provided between a stripe-shapedupper bus electrode and a stripe-shaped spacer electrode at least in animage display area; wherein said upper electrode formed as a film insaid image display area is connected to said upper bus electrode andseparated from said spacer electrode; wherein said upper electrode isisolated from said spacer electrode and said upper bus electrodes ofsaid thin film type electron sources present in adjacent rows (orcolumns); wherein spacers for supporting said cathode substrate and saidfluorescent screen substrate therebetween are disposed on said spacerelectrode.
 7. A display device comprising: a display panel comprised ofa cathode substrate and a fluorescent screen substrate, said cathodesubstrate including an array of thin-film type electron sources eachhaving a lower electrode, an upper electrode and an electronaccelerating layer retained between said lower electrode and said upperelectrode, each of said electron sources radiating electrons from saidupper electrode in response to a voltage applied between said lowerelectrode and said upper electrode, said fluorescent screen substrateincluding a fluorescent screen in which phosphors excited by saidelectrons to thereby emit light are formed; and a drive circuit fordriving said lower electrode and said upper electrode; wherein each ofsaid thin film type electron sources is provided between a stripe-shapedupper bus electrode and a stripe-shaped spacer electrode at least in animage display area; wherein said upper electrode formed as a film insaid image display area is connected to said upper bus electrode andseparated from said spacer electrode by a step of an appentice structureformed in a side surface of said spacer electrode; wherein said upperelectrode is isolated from said spacer electrode and said upper buselectrodes of said thin film type electron sources present in adjacentrows (or columns); wherein spacers for supporting said cathode substrateand said fluorescent screen substrate therebetween are disposed on saidspacer electrode.
 8. A display device comprising: a display panelcomprised of a cathode substrate and a fluorescent screen substrate,said cathode substrate including an array of thin-film type electronsources each having a lower electrode, an upper electrode and anelectron accelerating layer retained between said lower electrode andsaid upper electrode, each of said electron sources radiating electronsfrom said upper electrode in response to a voltage applied between saidlower electrode and said upper electrode, said fluorescent screensubstrate including a fluorescent screen in which phosphors excited bysaid electrons to thereby emit light are formed; and a drive circuit fordriving said lower electrode and said upper electrode; wherein each ofsaid thin film type electron sources is provided between stripe-shapedfirst and second upper bus electrodes at least in an image display area;wherein said upper electrode formed as a film in said image display areais connected to said first and second upper bus electrodes; wherein astripe-shaped third electrode is further provided at least in said imagedisplay area so as to be formed in parallel with said first and secondupper bus electrodes; wherein said upper electrode is separated by astep of an appentice structure formed in a side surface of said thirdelectrode, and isolated from said upper bus electrodes of said thin filmtype electron sources present in adjacent rows (or columns); whereinspacers for supporting said cathode substrate and said fluorescentscreen substrate therebetween are disposed on said third electrode.
 9. Adisplay device according to any one of claims 1 to 4 and 6 to 8, whereinsaid upper bus electrode includes a non-stripe-shaped portion outsidesaid image display area.
 10. A display device according to any one ofclaims 1 to 4 and 6 to 8, wherein each of said stripe-shaped upper buselectrode and said stripe-shaped spacer electrode has a laminated filmstructure of at least two layers of metal thin films.
 11. A displaydevice according to any one of claims 1 to 4 and 6 to 8, wherein each ofsaid stripe-shaped upper bus electrode and said stripe-shaped spacerelectrode is formed out of at least three metal films in which Cu is putbetween other metals.
 12. A display device according to any one ofclaims 1 to 4 and 6 to 8, wherein each of said stripe-shaped upper buselectrode and said stripe-shaped spacer electrode is formed out of atleast three metal films in which Cu is put between other metals, and alower film and an upper film of said at least three metal films are madeof Al, Cr, W, Mo, or an alloy of those metals.
 13. A display deviceaccording to any one of claims 1 to 4 and 6 to 8, wherein each of saidstripe-shaped upper bus electrode and said stripe-shaped spacerelectrode is formed out of at least three metal films in which Cu is putbetween other metals, and a lower film and an upper film of said atleast three metal films are made of Al, Cr, W, Mo, or an alloy of thosemetals, while said upper film of said at least three metal films isthicker than said lower film.
 14. A display device according to any oneof claims 1 to 4 and 6 to 8, wherein said stripe-shaped upper buselectrode and said stripe-shaped spacer electrode are used as scanninglines for matrix driving of said display panel.
 15. A display deviceaccording to any one of claims 1 to 4 and 6 to 8, wherein saidstripe-shaped upper bus electrode is formed out of a laminated film of athin film formed by sputtering and a conductive thick film formed byprinting.
 16. A display device according to any one of claims 1 to 4 and6 to 8, wherein a thin film portion of said upper bus electrode iscomprised of at least two films, having a step structure to connect withsaid upper electrode on one side surface of wiring of said upper buselectrode, and having an appentice structure to separate said upperelectrode on the opposite side surface of said wiring of said upper buselectrode.
 17. A display device according to any one of claims 1 to 4and 6 to 8, wherein said stripe-shaped upper bus electrode is formed outof a laminated film of a thin film formed by sputtering and a conductivethick film formed by printing, and said conductive thick film is anelectrode containing Ag.
 18. A display device according to any one ofclaims 1 to 4 and 6 to 8, wherein said stripe-shaped upper bus electrodeis formed out of a laminated film of a thin film formed by sputteringand a conductive thick film formed by printing, and said conductivethick film is an electrode containing Ag, while said upper bus electrodeis used as a scanning line for matrix driving.